Hello World!

2nd evaluation is finished now and I have passed the evaluation. My college will be starting from tomorrow i.e August 1st after a 3 month long summer break and I have completed most of my work on this project. I can still give around 25-30 hours per week. As a bonus work, I am trying to port python-casacore from boost::python to pybind11. Well I have hinted you this in some of my earlier posts but I haven’t told you formally. Have I?

boost::python works very well for python-casacore, but it has proven to be exceedingly annoying while building. It takes great care to ensure a fully consistent boost and python install and that python-casacore finds the right ones. Also, according to the issue #96 , this bug of boost seems to affect casacore. It would be great to remove this headache.

Why pybind11?

Although there are many options to wrap casacore, but we have chosen pybind11 for wrapping. I don’t know much about the other options but cython is one of the options. After watching this video, I really like it. One major benefit is that you can generate code for a python module file and check that into the repository so that the users don’t even need cython to build python-casacore . It uses a python-like language to compile to these C/C++ modules. If I was starting writing python-bindings for casacore from scratch, I would probably use it. However, cython has a different mentality to wrapping classes than boost::python, and converting python-casacore over would require a massive undertaking. This would take a lot of work, and I’m not sure I want to do that. Things are fine wrapped the way they are, as we get massive amounts of code reuse with one python super class that works via duck-typing with many different types of sub-classes. When interacting with C++ classes, cython requires strong typing. pybind11 looks like an interesting alternative. It is modeled on boost::python, but implemented as a header-file only solution which we could embed in python-casacore. It uses C++11 features to achieve this. C++11 as a dependency won’t be a major problem for casacore as in any way, however it will be a dependency in casacore 3.0(https://github.com/casacore/casacore/issues/580).


Pros Cons
Generate standards compliant C++ code Wrappers can instantiate templates, but only explicitly.
Write wrapper in a python-like language Strong typing in cython files required when interacting with c++. Either we add an additional layer of wrapping, or get a lot of duplicate code.


Pros Cons
Minimal effort to port python-casacore, as the syntax is almost identical to boost::python Requires C++11.
Header file only, can embed.  
Python version binding is at compile time, no more need to get consistent boost::python and python versions linked to casacore.  

I have found this to be pretty useful resource for shifting from boost::python to pybind11 and hope to make it more updated and will post the updated conversion table from boost::python to pybind11 on my future posts.

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